Roger Tanner Comes Home.

by David SnyderPrinted in Reflections: October, 2002.

On July 26, 2002 we had a special meeting of the Lowbrows. Roger
Tanner was the guest speaker. Until
a few years ago, Roger was an engineer at Ford and an active member of
the Lowbrows. That is, until
he decided to devote more time to astronomy. He moved to Arizona
with the goal of turning a hobby
into a full time job. Since that time he has worked on several unmanned
space missions. Roger comes
back to Ann Arbor every so often, and this time he brought a prototype
of a Mars Camera.

Roger had been given the assignment of designing a camera that may be part
of a mission to Mars. I
say “may be” because this is one of several possible missions,
only one of which will be selected. If
it is selected, a spacecraft will be launched in 2007 that will carry a
group of identical landers.
Each lander will be about the size of a coffee can and will be sent to
landing sites evenly
distributed across the Martian surface. Each lander will contain,
among things, one of Roger’s
cameras. These cameras will produce images of everything visible
within a 360-degree radius. A single
circular image will show everything on the ground and in the sky.
The purpose of the camera is to
detect changes in the atmosphere over a period of several years.

Roger discussed a number of issues involved with sending a spacecraft to Mars.
First of all the equipment must be able to withstand the acceleration of launch.
It then must deal with radiation, large temperature changes and the deceleration
of the landing. The craft also needs to deal with dust. Martian
dust is everywhere, and is a continual problem facing anyone involved with Mars
exploration. The dust potentially can get into anything that lands on
the Martian surface and possibly damage it.

Many of these issues can be tested on the ground, including how equipment
reacts to temperature
changes and exposure to radiation. However it is hard to test how
some pieces of equipment will react
to the dust. We know the dust has the form of a very fine-grained
powder. It is probably made of iron
oxides along with some other material, but the exact composition is not
known. The dust can
potentially stick to the surfaces of camera lenses, which could distort
the images. Since the camera
is supposed to function for several years, accumulated dust could be a
problem. The cameras aboard
the Viking Landers rotated in a “jerky” fashion that probably
helped dislodge any accumulated dust.
This will not help Roger’s proposed camera, since it has no moving parts.
The lens of the camera is
made of conductive material and is contact with the metal skin of the craft.
It is hoped that this
will electrically ground the lens and prevent it from accumulating a static
charge that could attract
dust. Even if some dust sticks to the lens, he felt that the dust
is likely to accumulate in a random
fashion and probably would not affect the data collection process.

Because budgets for space missions are tight, weight must be kept to an absolute
minimum (each pound dramatically increases the cost of a mission). Using
careful design, the electronics were simple and used minimal power. This
resulted in a lighter spacecraft. The camera fits onto a single chip surface
mounted onto a circular circuit board. Other types of cameras would have
given more resolution, but would have required more circuitry. The computer
and the camera use the same voltage supply, which reduces weight. The
computer was designed to wake up periodically, ask the camera to take a picture,
record the image and go back to sleep. Periodically it uploads data to
the orbiting spacecraft that in turn forwards it to earth. It had an ephemeris
to determine the best time to transmit. This minimizes transmission time
(which is big power drain). If the lander cannot talk to the orbiter,
it will continue to save data until it can. Even if an orbiter completely
failed, the lander will keep saving data until a new orbiter could take its
place.

There was also a brief discussion of manned Mars missions. Roger felt
such a mission was still years into the future. However recent indications
of water ice on Mars would make a Mars mission much easier (astronauts would
not have to bring as much water with them, water would add to the weight and
the cost of a possible manned mission). It also means that a supply of
oxygen is available (it is easy to produce oxygen if you have a plentiful source
of water). Oxygen would be used for breathing and as an oxidizer; the
rocket that would send the astronauts back to earth needs oxidizers of one form
or another.

Roger’s talk was two months ago, so I asked Roger for an update, he sent me
the following e-mail:

“I am writing up the project report. We are not doing any more
work at present. We are waiting for the next round of selections to
be announced in December. If we make it into the final 4 there, we will
do more work on all the proposals we are on. Just wait and see.
I have some other small projects to do for some research that the boss is
doing. Other than that it’s pretty slow.”

Photos

Roger Tanner

Roger is sitting and the camera is in the foreground.

The Mars Camera

A closeup of the Mars Camera.

Photo Credits

All the photographs on this page were taken by Dave Snyder during the special
club meeting described above.